Looking for a positive ID on a Serrasalmus species.

This is my fish; his name is Darwin. He's obviously a serra. I bought him at about 5". He's about 6" or so now. I've tried to get conclusive ID on him 3 times before. I bought him as a Serrasalmus marginatus. Most people I have met think he's a S. compressus. I must admit I think he's an S. compressus myself. Frank from OPEFE looked at it and thought the pics weren't good enough, to wait a year and take more pics. It's been about 3 or 4 months I think since then. Maybe we could give it another shot?

He's from Brazil. He cost about $60.00. He was labeled S. marginatus.. His fins were frayed when i got him. I added tonic salt one time and his color and fins improved. I haven't added salt since then.





POTM winner:




Any ideas?

bizump

Cam wrote:I hate to say it, but i really can't say for sure between the 2,..
Body characteristics are so similar that there is still some debate
weather Marginatus are actually a separate species or just regional
variants of Compressus. Both fish are collected in Brazil, so, unless
you know or can find out the river it was collected from,..everything
else will be best guesses i'm afraid. One thing i can tell ya, he's
an Awesome looking Serra!!

thanks cam. That's pretty much the same thing frank said. Looks like I may never know what he is. There are a few things that indicate comp over marginatus. They are as follows:

Caudal fin pattern: Darwin has a black band proximal to the caudal puduncle, a large area of hyaline tissue, and sometimes a black terminal band on the caudal fin. This is indicative of 3 species that I know of, compressus, alutvei, and eigenmanni (or humeralis.) The marginatus on the other hand has a dark V proximal to the caudal peduncle and that V extends all the way to the end of the fin tips on either direction. The rest of the caudal fin is hyaline tissue.

3rd and 4rth ray extensions on dorsal and anal fins: This is the most obvious difference. S. marginatus displays an elongated 3rd and 4th fin ray on the dorsal and anal fins. This extension causes the fin to elongate and take on a hooked apearance. This trait is not present in my fish. I thought it came with maturity, but apparently several marg keepers have told me their margs had it from like 4 inches on.

Localized pgimentation: His spots morph from spots to bars regularly, sometimes they extend almost to the serrae, most times they are well proximated above the lateral line. They usually look like elongated spots or bars. This is indicative of those 3 species more so than marginatus whose spotting is round, small, and extended well below the lateral line. Altuvei's usually have pigmentation well below the lateral line also.

He's not quite laterally compressed enough to be an eigenmanni. His shape is much more characteristic of altuvei or compressus. Because he was shipped from brazil, it's much more likely that he is a compressus, rather than altuvei as the latter are localized to venezuela.

These are just some theories I have developed trying to ID my fish. If anybody has an thoughts please feel free to share.

Thanks,
-C

come on I know we've got more Piranha people on here than this. Thanks for the look cam. Anyone else? Please?